Technical Abstract:
Rotation crops with potential disease-suppressive properties have been evaluated for their efficacy in reducing persistent soilborne diseases and enhancing crop productivity in various field trials over the last several years in Maine. Rotation crops assessed included several with biofumigation potential, such as Brassica spp. (canola, rapeseed, radish, turnip, various mustards and mustard blends) and sorghum-sudangrass hybrids, as well as other small grain and grass crops (barley, buckwheat, ryegrass, and winter rye), and were evaluated as full-season crops, green manures, and fall cover crops in 2- and 3-yr cropping systems. Although results varied somewhat from field to field and year to year, consistent reductions in soilborne diseases were observed with several rotations. Canola and rapeseed rotations consistently reduced black scurf and common scab by 30-80% relative to other 2-yr rotations. Canola and ryegrass rotations, and rapeseed and mustard green manures, reduced powdery scab by 15-50% in various trials. One season of a mustard blend and sorghum-sudangrass green manure crop reduced Verticillium wilt (early dying) by 20-25% in a severely infected field, and also significantly increased tuber yield. A 3-yr disease-suppressive rotation featuring mustard blend and sudangrass green manures reduced all observed soilborne diseases by 20-50% compared to other 2- and 3-yr rotations. Addition of a winter rye cover crop after most rotations further reduced diseases by 10-20%. This research demonstrated that effective rotations can substantially reduce soilborne disease problems, but cannot completely control them. Good rotation strategies should be used in conjunction with other crop and soil management approaches to achieve more sustainable crop production.